Performance of the Liquid Argon Calorimeter

The Liquid Argon calorimeter (LAr) is a key detector component in the ATLAS experiment at the LHC. It provides precision measurements of electrons, photons, jets and missing transverse energy produced in the LHC proton-proton collisions. The calorimeter system consists of an electromagnetic barrel calorimeter and two endcaps with electromagnetic (EMEC), hadronic (HEC) and forward (FCal) calorimeters. The lead-liquid argon sampling technique with an accordion geometry was chosen for the barrel electromagnetic calorimeter (EMB) and adapted to the endcap (EMEC). A presampler (PS) is installed in the cryostat in front of the EM calorimeter to provide a measurement of the energy lost upstream. The hadronic endcap calorimeter (HEC) uses a copper-liquid argon sampling technique with plate geometry. Finally, the forward calorimeter (FCal) is composed of three modules featuring cylindrical electrodes with thin liquid argon gaps. The barrel and the two endcaps are housed into three cryostats kept at about 87 K. We present results assessing the liquid argon calorimeter performance obtained using random triggers, calibration data and LHC proton-proton collisions. Properties of the read-out channels such as pedestal, noise and gain have been measured and show the high stability of the LAr electronics over several months of data taking. The first physics results concerning key calorimeter variables such as photon identification, electrons, a nd missing tranverse energy are also shown.